The present invention relates generally to high resolution and high chromaticity color monitors and televisions. More particularly, the present invention relates to a novel digital system for providing the color convergence function for color monitors and televisions and for providing synchronization to a color signal and external clock.
In many military and industrial raster-scanned monitor applications, it has been found to be beneficial to display the monitored information on a video screen as color-coded graphics and alphanumeric data. While there are definite advantages to displaying color-coded data in military command and industrial control situations, such advantages could not heretofore be realized because, owing to the amount of data to be displayed on the screen, color monitor displays were not capable of sufficient resolution and color purity.
In fact, heretofore, monochrome video monitors actually outperformed conventional color displays in such areas as sharpness and legibility of data over the entire display surface; color control, convergence and reproducibility; adaptability to the human operator; immunity to shock and vibration; and performance stability over time.
In order to provide for the effective display of multi-colored data and graphics on a color monitor, the monitor must produce very high true visual display resolution and accurately reproducible colors. The colors produced must be free of visible jitter, drift and misconvergence, on the entire display surface of the monitor screen, including the edges and corners. In such manner, the display parameters are controlled to optimize the ability of the operator to read the color-coded display data. In addition, such accuracy of display must frequently be maintained under adverse environmental operating conditions.
The achievement of such characteristics provides high legibility and accurate reading of high density display data typically found in military command and control applications. In such applicatins, as well as various other industrial and transportation control enterprises, characters, complex symbols and other details must be small to minimize the overlapping and unreadability of the data. The display quality of monitors built to achieve the above characteristics equals or surpasses that of the best monochrome monitors of comparable size, while providing the additional benefits of color-coding.
Military command and control systems are increasingly required to cope with dense target environments requiring rapid processing, display and decision-making on large amounts of data. The display system must present the data to the operator in a form which enables him to quickly and accurately identify and track items of interest amid the clutter and overlapping of many or similar-appearing items. Further, such items are constantly changing positions, with the frequent, random appearance of new items, usually near the edges of the display.
Color-coding of the display data can improve operator accuracy, shorten his reaction time and lessen his fatigue, serving as a highlighter and an aid to discrimination of similar-appearing data in a dense display. Such benefits have encouraged increased use of color displays, both in military applications, and also civilian activities, such as air traffic control systems.
Prior to the present invention, several parameters of color display performance have been less then satisfactory than those of monochrome displays for such usage. The present invention has resulted in significant improvements that are necessary in order to achieve any benefit from the addition of color-coding. Such improvements are in the areas of legibility, that is, the crispness and readability of the data; chromaticity, that is, color control for optimum human perception and readability; and color convergence, that is, the coincidence of position of primary colors and performance stability over time. The color monitor described generally, and the convergence circuit specifically described herein, achieve such performance goals.
The digital convergence and synchronization circuitry of the present invention is designed to provide a highly legible display, as well as to display selected colors controlled to close tolerances. The three primary colors, red, green and blue, are converged to within less than a line thickness. That is, misconvergence of approximately 0.015 inch for an 0.018 inch line thickness is achieved. Unlike prior art color monitors, the present invention achieves such performance over the entire display area, not just a center "quality circle" area of the display.
The above-described legibility is achieved according to the present invention by providing a uniform spot size of 0.015 inch without Moire effects and a color misconvergence of less than approximately 0.012 inch over the entire display surface, including the edges. Such values are achieved regardless of operator settings of the brightness and contrast controls. The effective resolution of the display is approximately 750H.times.1000V, or 750,000 pixels, on a nominal 11 inch H.times.14 inch V display.
Conventional monitors do not meet such legibility criteria since typical spot size averages about 0.025 inch and misconvergence can be up to 0.040 inch over the entire display surface. Typical specifications for those monitors which describe their resolution as 1280H.times.1024V actually indicate the addressability or number of spot positions, rather than resolution (visual discrimination of adjacent spots). In reality, the true resolution of such monitors is about 600H.times.450V, or 270,000 pixels, or about one-third of that achieved by the color monitor of the present invention. Furthermore, misconvergence can further degrade that resolution and hence the legibility near the periphery of the display.